extension property to selectively escalate warnings to errors

Daffodil issues warnings about things like 

• when two element children differ only by namespace so that JSON (or other form that does not support namespaces) won't work.

Such a warning should be something we can escalate to an error, by way of a property in the schema - such property indicates an intention to maintain the schema in a manner that keeps it compatible with JSON (or whatever).

There are other warnings that should also be escalated to errors. (see DAFFODIL-2736, DAFFODIL-2737)

One should be able to selectively choose which warnings to escalate to errors.